Origins of Multi-decadal Variability in Sudden Stratospheric Warmings

Abstract

<p>Sudden Stratospheric Warmings (SSWs) are major disruptions of the Northern Hemisphere (NH) stratospheric polar vortex and occur on average approximately 6 times per decade in observation based records. However, within these records, intervals of significantly higher and lower SSW rates are observed suggesting the possibility of low frequency variations in event occurrence. A better understanding of factors that influence this decadal variability may help to improve predictability of NH mid-latitude surface climate, through stratosphere-troposphere coupling. In this work, multi-decadal variability of SSW events is examined in a 1000-yr pre-industrial simulation of a coupled Atmosphere-Ocean-Land-Sea ice model. Using a wavelet spectral decomposition method, we show that hiatus events (intervals of a decade or more with no SSWs) and consecutive SSW events (extended intervals with at least one SSW in each year) vary on multi-decadal timescales of period between 60 and 90 years. Signals on these timescales are present for approximately 450 years of the simulation. We investigate the possible source of these long-term signals and find that the direct impact of variability in tropical sea surface temperatures, as well as the associated Aleutian Low, can account for only a small portion of the SSW variability. Instead, the major influence on long-term SSW variability is associated with long-term variability in amplitude of the stratospheric quasi biennial oscillation (QBO). The QBO influence is consistent with the well known Holton-Tan relationship, with SSW hiatus intervals associated with extended periods of particularly strong, deep QBO westerly phases. The results support recent studies that have highlighted the role of vertical coherence in the QBO when considering coupling between the QBO, the polar vortex and tropospheric circulation.</p>

Interaction between decadal‐to‐multidecadal oceanic variability and sudden stratospheric warmings

“…Apart from multidecadal oceanic variability, we acknowledge that there might be other sources of long-term SSW variability, such as multidecadal variability in the amplitude of the QBO 8 or ENSO. As previously mentioned, a QBO is not present in the MPI-GE because of the relatively low vertical resolution of this version of the atmospheric model.…”

“…6 Indeed, a few modeling studies have suggested the existence of low-frequency variability of SSWs. 7,8 However, the short observational data record does not allow the full characterization of their long-term variability. In addition, other issues have arisen, such as the computational cost of running long simulations using models with a well-resolved stratosphere and the storage required for the daily output needed for the identification of SSWs.…”

A wavelet transform method to determine monsoon onset and retreat from precipitation time‐series

“…This article introduces a wavelet transform method to determine monsoon onset and retreat dates using pentad‐mean precipitation time‐series. Wavelet algorithms have been extensively used in atmospheric research for multiple purposes, such as the detection of the boundary layer height (e.g., Brooks, 2003), as well as to analyse time‐frequency features of a signal (e.g., Whitcher et al ., 2000; Dimdore‐Miles et al ., 2021). In fact, Allen and Mapes (2017) used a wavelet analysis to determine monsoon onset and retreat using daily OLR data.…”

Decadal Amplitude Modulations of the Stratospheric Quasi-biennial Oscillation

“…Kawatani et al (2019) reproduced realistic differences in the QBO between El Niño and La Niña by performing a 100-year simulation, respectively, of an atmospheric general circulation model under each SSTa condition. However, Dimdore-Miles et al (2021), analyzing a 1000-year simulation of a coupled global climate model, showed that multi-decadal QBO amplitude variations are seemingly linked sporadically with Niño 3.4 SSTa.…”